The present invention pertains to a process for the production of vinyltoluene, and more specifically to a method for inhibiting the formation of undesirable thermal polymers in the manufacture of vinyltoluene.
Vinyltoluene is commonly prepared by the catalytic dehydrogenation of ethyltoluene, cooling of the gaseous materials to condense the same and fractionally distilling the liquid product to obtain vinyltoluene. In the manufacture of vinyltoluene by the catalytic dehydrogenation of ethyltoluene, considerable difficulty has been experienced prior to and during the distillation of the crude vinyltoluene product to obtain purified vinyltoluene, because of the production of thermal polymers. This problem manifests itself in a plugging of the equipment used for the manufacture of the vinyltoluene.
In order to prevent the formation of the thermal polymer during distillation of vinyltoluene, various types of known polymerization inhibitors have been employed in connection with prior art distillation processes. These inhibitors have been only partially effective in preventing the formation of the undesirable thermal polymer in the distillation apparatus. However, since this normal addition of inhibitor to the crude vinyltoluene product takes place in or just prior to the distillation apparatus, the inhibitor does not prevent the formation of the undesirable thermal polymers in the equipment upstream of the distillation unit, such as in the condensers and in the crude vinyltoluene drum. The occurrence of fouling in the condensers and drum due to polymer formation represents a serious problem in the production of vinyltoluene.